The present invention is a novel modem and interfacing system that permits connection of a single cellular-capable modem to a variety of cellular transceivers or to a landline telephone jack.
In the prior art, modems specifically designed for cellular use were designed to connect to a single type of cellular bus. For example, the inventor's prior U.S. Pat. No. 4,697,281 describes one of the earliest commercially successful cellular modems. This modem includes integral interfacing software and hardware that is specific to the type of cellular transceiver used with the modem. Thus, a modem designed to work, for example, with a Motorola transceiver will not operate with an Oki transceiver. It would be desirable to develop a system that would permit a single, generic modem to operate with a variety of transceivers.
These prior art modems also are not designed to interface conveniently with a landline telephone jack. To interface with a landline telephone jack, these modems would have to be provided with separate landline connection hardware and operating software, adding cost and complexity. Because cellular modems are relatively expensive, it would be desirable to use a single modem for a variety of mobile and fixed-station data transmission tasks. The inability of a single modem to function easily in both environments is particularly troublesome when the modem is installed internally in a portable computer. If a portable computer is equipped with a modem that operates only in the cellular environment, an auxiliary modem must be provided to allow data transmission when the portable computer is used in an office setting. Similarly, if the portable computer's internal modem is not cellular-compatible, a separate cellular modem must be carried with the mobile unit. The need to carry a separate cellular modem with significant weight and dimensions reduces the convenience and portability, and thus the usefulness, of the portable computer/cellular telephone combination. Therefore, the lack of landline capability is a significant disadvantage for cellular modems.
The prior art includes systems which are distantly related to the system of the present invention, but none of these prior art systems provides a method of selectively connecting a single cellular-capable modem to a variety of cellular transceivers or to a landline telephone jack.
Some prior art interfacing systems, which will be referred to as telco emulators, permit operative connection of a variety of ordinary analog telephone sets to cellular transceivers by simulating a landline telephone connection. Such systems are disclosed in U.S. Pat. Nos. 4,737,975 to Shafer, 4,775,997 and 4,658,096 to West, Jr. et al., and 4,718,080 to Serrano et al. U.S. Pat. No. 4,012,596, also to West, Jr. et al., shows a similar system for connecting an ordinary telephone device to a simplex radio system. U.S. Pat. No. 4,887,290 to Dop et al. shows a cellular alarm backup system which can selectively connect either ordinary house phones or a digital alarm communicator to a cellular transceiver. It should be noted that, for reasons explained in the inventor's prior U.S. Pat. No. 4,697,281, an ordinary home or office modem will not function properly in a cellular environment.
Telco emulators have been used to connect modems to cellular transceivers. For example, U.S. Pat. No. 4,837,800 to Freeburg, et al. shows a telco emulator, the Motorola "CELLULAR CONNECTION," used to connect a cellular modem to a cellular transceiver. However, the telco emulator suffers from a high cost of production. These emulators must provide for Tip and Ring current, ringing voltage, and DTMF (touch-tone) reception and decoding. Each of these functions adds cost and complexity to the telco emulator. Further, the telco emulator must address the special dialing needs of the cellular transceiver, such as generating a SEND command. The telco emulator is also incapable of returning detailed status information and data from the cellular telephone to the connected device, since the telco emulator assumes that the device is not programmed to operate in a cellular environment. As a result of all these factors, the telco emulator method provides suboptimal control of the cellular transceiver in cellular modem applications as compared to the system of the present invention.
Radiotelephone interfacing systems not related to modems have also been developed in the prior art. U.S. Pat. No. 4,852,146 to Hathcock et al. shows an auxiliary dialing system that connects between a cellular handset and a cellular transceiver, but this system does not connect a generic device to a specific cellular transceiver. U.S. Pat. No. 4,752,949 to Steinbeck et al. discloses an interface system for connecting a cordless telephone to a base unit by installing a cord. The cord includes both data signal lines and control lines.
It is well-known in the landline PBX art to transmit both digital control and analog information signals through the same connector in a modular telephone wiring system. Some of these systems, as exemplified by the system disclosed in U.S. Pat. No. 4,759,059, allow ordinary analog telephone devices to connect to a digital telephone system. The analog devices then use analog lines of the telephone system but are not connected to digital control lines of the telephone system.
Finally, it is also known to connect a plurality of telephone units to one or more cellular transceivers, as illustrated in U.S. Pat. Nos. 4,890,315 to Bendixen et al. and 4,568,800 to Orikasa.
However, none of the prior art systems disclose a single, cellular-capable modem and cost-effective means that permit selective connection of the modem either to a variety of cellular transceivers or to a landline telephone jack.